Sunday, February 26, 2017

The Lamina Dura



The lamina dura is the bony lining of the socket (alveolus) of a tooth. The periodontal ligaments extend from the lamina dura to the cementum of the tooth, an keep the tooth in place. The lamina dura is cribriform plate produced by the periodontal ligament and fibers of the periodontal ligament are embedded within it.

While loss of the lamina dura (arrow in image above) is sometimes said to be pathognomonic for hyperparathyroidism, it can be seen in a wide range of conditions:
  • Hyperparathyroidism: The case above is from a patient with primary hyperparathyroidism.
  • Osteomalacia
  • Osteoporosis
  • Paget disease
  • Leukemia
  • Myelomatosis
  • Cushing disease


The lamina dura can be thickened in bisphosphonate-related osteonecrosis of jaw (BRONJ)

References

Sunday, February 19, 2017

Systemic Mastocytosis


Systemic mastocytosis (SM) refers to mast cell infiltration in extra-cutaneous tissues. The symptoms of systemic mastocytosis are due to degranulation of mast cells and/or accumulation of mast cells in target organs.

Degranulation of mast cells

Symptoms can be caused by secretion of the following factors:
  • Histamine: Pruritus, urticaria, hypotension, gastric hypersecretion, bronchoconstriction.
  • Heparin: Local anticoagulation, osteoporosis
  • Leukotrienes: Bronchoconstriction
  • Prostaglandins: Bronchoconstriction, flushing
  • Platelet-activating factor:
  • Proteases:
  • Tumor necrosis factor:

Accumulation of mast cells in organs

Accumulation of mast cells in organs can cause organ dysfunction. The so-called B findings refer to organ involvement without organ dysfunction. C findings refer organ involvement with organ dysfunction. The example above shows hepatic involvement with cirrhosis (white arrow) and ascites (yellow arrow) and nodal involvement with bulky adenopathy (red arrow). We also have involvement with diffuse sclerosis. Interestingly, the non-radiology literature stresses the more common osteoporosis, with scarce mention of the sclerosis that tends to dominate the radiology literature.

Diagnosis systemic mastocytosis

The diagnosis of SM requires either, 1 major and 1 minor OR 3 minor criteria. Warning: Boring for radiologists

The one major criterion is: Multifocal, dense infiltrates of mast cells (≥15 mast cells in aggregates) in sections of bone marrow and/or other extra-cutaneous organ(s).

Minor criteria are:
  • Bone marrow or other extra-cutaneous organs: >25% of mast cells in the infiltrate are spindle-shaped or have atypical morphology, or of all mast cells in bone marrow aspirate smears, >25% are immature or atypical.
  • Activating point mutation at codon 816 of KIT in bone marrow, blood, or another extra-cutaneous organ.
  • Mast cells in bone marrow, blood, or other extracutaneous organs express CD2 and/or CD25 in addition to normal mast cell markers.
  • Serum total tryptase persistently > 20 mg/mL (unless associated w clonal myeloid disorder).

Subtypes

  • Indolent (ISM): No C findings
  • Smoldering (SSM): 2+ B findings, no C findings
  • Aggressive (ASM): C findings, no MCL features*
  • Mast cell leukemia (MCL): BMBx diffuse infiltration by atypical, immature mast cells. Aspirate smears ≥20% mast cells.
  • SM with associated hematologic neoplasm (SM-AHN): SM + MDS, MPN, AML, lymphoma, other

References

Akin C, Gotlib J. Systemic mastocytosis: Determining the subtype of disease. UpToDate

Sunday, February 12, 2017

The Cervical Split: A Pseudofracture


A horizontal line projecting over a cervical vertebral body on lateral radiographs can simulate a fracture or a butterfly vertebral body. This pseudofracture, the so-called cervical split, can result from the lucency between contiguous uncovertebral osteophytes, or, as in the case above, cervical scoliosis resulting in projection of the facet joint over the vertebral body.

A cervical split due to uncovertebral joint osteophyte formation is said to be always accompanied by disc space narrowing.

References

Thursday, February 2, 2017

Chronic Subperiosteal Iliac Hematoma



Subperiosteal iliac hematoma is caused by traumatic avulsion of the periosteum in children and young adults. The loose attachment of periosteum in young patients allows it to be displaced by hematoma in trauma. In the chronic phase, it is typically incidentally discovered by radiologists.

In the chronic phase, it presents as a lens-shaped ossified process on the internal aspect of the iliac wing with a ghost cortex (dotted line in the image above). It may or may not have the well-defined central lesion we have in this case.

References

Guillin R, Moser T, Koob M, Khoury V, Chapuis M, Ropars M, Cardinal E. Subperiosteal hematoma of the iliac bone: imaging features of acute and chronic stages with emphasis on pathophysiology. Skeletal Radiol. 2012 Jun;41(6):667-75.

Wednesday, December 21, 2016

M.D. = Makes Decisions (unless you're a radiologist)

#
1 This is a cat. This is a hemangioma.
2 This is most likely a cat. This is most likely a hemangioma
3 This is consistent with a cat. This is consistent with a hemangioma.
4 This is most likely a cat, but get a follow-up picture to make sure it wasn't a baby tiger all along. This is most likely a hemangioma. Recommend follow-up to document stability.
5 This is most likely consistent with a cat. This is most likely consistent with a hemangioma.
6 This is likely a cat, but can't exclude a tiger hiding behind it way in the distance. This is likely a hemangioma, but can't exclude malignancy, sarcoid, etc.
7 This is likely a cat. Why don't you take a look for yourself and stop bothering me? This is likely a hemangioma. Recommend clinical correlation.
8 This is likely a cat, but get a saliva sample and send it in for genetic analysis. Better yet, kill the cat and dissect it. This is likely a hemangioma. Recommend biopsy. Open biopsy may be required.


In the real world (with the cat), anything other than statement #1 will get you laughed at. In radiology, statement #1 is rare. Instead we teach our residents and fellows, by our own weak examples, to be as non-declarative as possible.

Statements #2 and #3 are as declarative as most radiologists get. "I said most likely. What more do you want from me?!"

Statement #4 just passes the buck to the next radiologist.

Statement #5 combines 2 mild hedge words to produce one super-hedgy sentence.

Statement #6 is the reason Bayes rolls in his grave every time a radiologist signs a report.

Statement #7 is basically saying, "Thanks for the money suckers! This report was useless." We have access to so much patient data these days that it baffles me to see this in reports. Of course, this doesn't apply to cases where we're reading in isolation and when the only history we get from referrings is "pain," or some random ICD code. This negligent absence of data in a requisition borders on (is?) malpractice. I've seen it in imaging referrals my family members get from their doctors and it aggravates me to no end.

Statement #8, I don't even... For a cat/hemangioma?

Look, sometimes we have to hedge. Sometimes we are no better than Plato's cave captives, squinting at shadows with no idea of what's behind us. We know that two or more widely disparate entities can have identical imaging features. But when you know something can only be one thing, just say so. Save the patient some anxiety. And, save the rest of us some money by reducing unnecessary imaging.

What are some of your favorite radiology hedges?

Wednesday, March 2, 2016

Mimicker: Inguinal Mesh Plug

Ryan Schwope mesh plug
Left inguinal mesh plug with a lobular contour

Ryan Schwope mesh plug cor
Left inguinal mesh plug. Note conical morphology on this coronal MPR.
  • Depending on the inguinal hernia repair method chosen, a mesh plug can be used for reinforcement. One such method uses a polypropylene (Prolene) plug
  • The post-operative appearance of an inguinal mesh plug can masquerade as an inguinal mass or lymphadenopathy

Imaging Findings

  • On CT, mesh plugs can have a slightly nodular or smooth outline. The density is similar to sightly lower than muscle. Mesh plugs have also been reported as a ring-like density with central fat attenuation, potentially mimicking epiploic appendicitis if on the left
  • On MRI, mesh plugs are typically T1 hypointense and demonstrate variable T2 weighted signal
  • Due to a granulomatous reaction, mesh plugs can be FDG avid

Helpful hints in preventing misdiagnosis

  • Mutliplanar reformations can be useful in demonstrating the conical morphology of the mesh plug, although they can appear ovoid 
  • Postsurgical changes including skin thickening and suceptabliity artifact can also be helpful imaging features

Saturday, January 16, 2016

Suspected Type I Rotatory Atlatoaxial Subluxation in Asymptomatic Patients

type I Atlantoaxial Rotatory Subluxation
In an earlier post on rotatory atlatoaxial subluxation, we discussed the Fielding and Hawkins classification, and its application to symptomatic patients (e.g., those with torticollis). Here, we discuss the challenge of making a diagnosis of rotatory atlatoaxial subluxation in unselected patients.

That is, what do you do if your neck or c-spine CT scan is obtained with the head turned, and you see what looks like a Type I rotatory atlatoaxial subluxation?

The patient below was referred to our institution in a cervical collar for management of atlantoaxial rotatory subluxation.
normal head rotation
30-year-old man: Thick reconstructions centered at C1-C2 from a CTA obtained with the head rotated to the left. There is apparent type I atlantoaxial rotatory subluxation.
 
Let's take a look at what we know:
  • Normal maximum rotation of the head on body is between 60–80°.
  • Normal maximum rotation of C1 on C2 makes up for about half of that: 30–45° (although some sources say it can be up to 50°).
  • Cutoff for abnormal C1-C2 rotation: >45° or >56°, depending on source.
Looking at our image above, our rotation of C1 on C2 is about 30 degrees, which puts it in the normal range. But, what if the number was higher? How well do we do as radiologists in correctly identifying this as normal?

One study that was helpful came from the forensic field. Pathologists had noted that CTs of cadavers, which are impossible to position "correctly," were resulting in a lot of over-calling of atlantoaxial rotatory subluxation. When they looked at their data they found:
  • 19 cases where the C-spine was stable on autopsy. In those 19, 13 had suspected rotatory subluxation based on on CT (false positives)
  • The C1-C2 angle in those 13 false positives were between 16–47°.
  • All false positives were type I.
  • 2 cases where the C-spine was unstable at autopsy. In those 2 cases, 1 had suspected rotatory subluxation on CT (true positive).
  • The C1-C2 angle in the 1 true positive was 42°.
  • There was a significant association between the false positives and degree of head rotation.

Generalizing this cadaveric study suggests that we need to be careful in calling type I atlantoaxial rotatory subluxation in asymptomatic patients who simply happen to have their head turned in the scanner. This supports the conclusions from a study in living, asymptomatic patients, where the authors showed that incomplete rotational facet displacement on CT was not sufficient to define subluxation.

References